America's Bill Haas produced an impressive 5-under-par final round Sunday to win the AT&T National by three shots in Bethesda, Md.

Haas was tied for top spot with compatriot Roberto Castro going into the final day's play at the Congressional Country Club but produced an almost flawless round to grab the fifth PGA Tour title of his career.

Haas shot six birdies, with one bogie, to finish at 66, 12 under for the tournament, enabling him to finish comfortably clear of Castro.

"It's so hard to win out here. It's pretty special," Haas said after his victory.

"It was important I get off to a good start. The putter felt great and saved me on the back nine a couple of times."

Castro was unable to match his countryman on the final day, despite being level at the end of the Saturday's play, but his round of 2-under ensured that he finished as runner-up.

South Korea's Lee Dong-hwan put in the performance of the day to reach third place. He finished 7-under to move 17 places up the leaderboard and tie at 8-under overall, alongside American Jason Kokrak.

Jordan Spieth, who was attempting to become the youngest PGA Tour winner since 1931 at 19 years old, ended up sixth after a final-round 70. He was 6-under for the tournament.

Spieth was part of a five-man tie at the top early in the day but was unable to keep up with Haas.

England's Brian Davis also made up plenty of ground on the final day thanks to a round of four under. That meant he was one of the biggest upwards movers of the day, climbing 19 places to tie at eighth.

He was joined by Canadian Graham DeLaet and Americans trio Morgan Hoffmann, Brandt Snedeker and James Driscoll.